The present invention relates to a multi-access communication system such as a bi-directional CATV network or passive optical star network where a center station dynamically allocates the band of an up-link to subscriber stations, and more particularly to a method for insuring the service quality on an uplink.
In the communication system including bi-directional CATV networks and passive optical star-networks, the downlink linked from a center station to subscriber stations generally is of a broadcast type while the uplink linked from a subscriber station to the center station is of a multi-access type using the time division multiplexing. The center station allocates an identifier when a subscriber station starts its operation. Next, when the subscriber station transmits up data to the center station, the center station first transmits up-band reservation permission information to a subscriber station group. Next, a subscriber station holding up data to be transmitted transmits reservation information formed of an identifier and a reserved up band to the center station. When pieces of reservation information simultaneously transmitted from plural subscriber stations collide with each other on the up line, the center station and the related subscriber stations solve the collision problem. Finally, the center station properly receives all pieces of reservation information. When holding data to be next transmitted at a data transmission time, the subscriber station adds the next reservation information to the up data and then transmits it to the center station. The center station creates up-band allocation information based on the reservation information and then informs the subscriber station of it. The subscriber station transmits the up data to the center station at an allocated up band. When the subscriber station does not require the service quality, the center station evenly allocates the up band to all subscriber stations every up transmission packet.
On the other hand, when the service quality which requires a band to be secured and the upper limit of a transmission delay amount as in the telephone and moving images communications is known, it is necessary to insure the service quality provided on the up-line every subscriber station. Conventionally, in order to insure the service quality on the up-multi-access line, the subscriber station informs the center station of a required service quality before transmitting up reservation information, whereas the center station periodically allocates the band for an up line in response to the service quality. When a plurality of up services are provided, the up-band allocation priority control is performed by specifying the service priority based on reservation permission information, reservation information or band allocation information and time-dividing the band of an uplink with the priority. As previous reports, there are xe2x80x9cIEEE Communication Magazinexe2x80x9d, written by James E. Dail et. al, pp. 104-112, March 1996 and xe2x80x9cIEEE Transactions on Communicationsxe2x80x9d, written by P. Papantori-Kazakos, Vol. 40, No. 3, pp. 541-555, March 1992.
Likewise the conventional multi-access communication system, the priority controlling method, which designates priority based on reservation permission information or band allocation information and then allocates an up band, requires to previously and fixedly determine various up-service-to-priority relationships between the center station and subscriber stations. Hence, the conventional system has disadvantage of being difficult to finely control the priority according to the up-service quality, thus lacking the flexibility.
Moreover, like the conventional multi-access communication system, there is the disadvantage in that when the center station insures the service quality by periodically allocating up-bands, the allocated up-band becomes wasteful. The reason is that when subscriber stations generate up data at irregular intervals, it often occurs that although the center station allocates the up-band of an uplink to a subscriber station, the subscriber station does not have up-data to be transmitted. Particularly, when the up-band data length is variable, it is difficult that the subscriber station accurately estimates an average up-data length to be reported. The problem is that when an average up-data length longer than the actual data length is reported, the up-band is excessively allocated and that when an average up-data length shorter than the actual data length is reported, the up-band allocation is delayed.
The objective of the present invention is to solve the above-mentioned tasks.
Moreover, the objective of the invention is to provide a multi-access communication system such as bi-directional CATV networks, passive optical star networks, or the like, where a center station dynamically allocates uplink bands to subscriber stations, can flexibly and effectively allocate uplink bands for the up-service quality assurance.
Furthermore, the objective of the present invention is to provide a method of flexibly and effectively allocating uplink bands in a multi-access communication system to insure the up-service assurance.
The objective of the first aspect of the present invention is achieved by a multi-access communication system comprising a center station including means for allocating identifiers to subscriber stations; means for transmitting reservation transmission permission information to the subscriber stations, means for receiving reservation information from a subscriber station; means for allocating an up band based on the reservation information from the subscriber station; means for receiving service quality request information from the subscriber station; means for allocating an identifier to a subscriber station according to a requested service quality; and means for allocating bands from data with higher priority according to the service quality designated by the identifier of reservation information from a subscriber station.
Moreover, the subscriber station includes means for receiving an identifier allocated from a center station; means for receiving reservation transmission permission information from the center station; means for transmitting reservation information to the center station at an up band designated with the reservation transmission permission information; means for receiving up-band allocation information from the center station; means for transmitting up-data to the center station at an up-band designated with the up-band allocation information; means for transmitting service quality request information to the center station; and means for adding an identifier according to the service type of the up-data to be transmitted and adding an identifier according to the service type of the up-data to be transmitted to reservation information to be transmitted to the center station.
In the multi-access communication system of the second aspect of the invention, the center station has means for periodically transmitting reservation transmission permission information to which the identifier of the service is added, to the subscriber station using a high priority service.
In the multi-access communication system of the third aspect of the invention, the center station includes means for allocating a unique identifier to each of the subscriber stations each using a high priority service and allocating a common identifier to a group of a subscriber station group using the high priority service, and means for periodically transmitting reservation transmission permission information to which a common identifier is added, to the subscriber station group using a high priority service, and the subscriber station includes means for transmitting reservation information for an up-band to the center station in response to the reservation transmission permission information if there is up-data to be transmitted corresponding to service designated by the identifier.
In the multi-access communication system of the fourth aspect of the invention, when the center station receives a new service quality request information from a subscriber station, the center station has means for allocating a new unique identifier to the subscriber station and means for allocating a common identifier to the subscriber station group using the same identifier. Moreover, when the subscriber station starts to use a new service, the subscriber station has means for informing the center station of the quality of the service, means for receiving a new unique identifier allocated by the center station, and means for receiving a common identifier allocated to the subscriber station group using the same service type.
In the multi-access communication system of the fifth aspect of the invention, the center station has means for periodically transmitting up-band allocation information to the subscriber station according to a service quality informed from the subscriber station, for periodically transmitting reservation transmission permission information with a unique identifier to the subscriber station, for periodically transmitting reservation transmission permission information to the subscriber station group, the subscriber station group including the subscriber station and using the same service, or for selectively performing a periodic transmission control to a service.
In the multi-access communication system of the sixth aspect of the invention, the center station has means for periodically measures an up-load received from said subscriber station; and means for periodically transmitting up-load allocation information to the subscriber station according to a measured up-load value, for periodically transmitting reservation transmission permission information to the subscriber station, the reservation transmission permission information having a unique identifier, for periodically transmitting reservation transmission permission information to the subscriber station group, the subscriber station group including the subscriber station and using the same service, or for selectively performing a periodic transmission control to the service.
Moreover, according to the present invention, a method of allocating uplink bands in a multi-access communication system, the multi-access communication system including a center station, subscriber stations, a broadcast downlink linked from the center station to the subscriber stations, and a multi-access uplink linked from the subscribers to the center station, wherein the center station previously allocates identifiers to the subscriber station, wherein a subscriber station having up-data to be transmitted transmits reservation information within a band permitted by the center station, the reservation information being formed of an identifier and an up-band to be reserved, wherein the center station allocates a band of the uplink to the subscriber station based on the reservation information, the method comprising the steps of previously issuing service quality assurances from the subscriber stations to the center station when the subscriber stations request the service quality assurance; allocating an identifier for each of the service assurances by means of the center station and then informing the subscriber stations of the allocation; transmitting, when the center station transmits the reservation transmission permission information to the subscriber stations, the reservation information by means of the subscriber stations by adding an identifier according to the service type of the up-data to be transmitted; and allocating up-bands from data with higher priority in decreasing order of priority by means of the center station according to the service quality designated by the identifier of the reservation information.
More specifically, in the multi-access communication system according to the first aspect of the invention, when first requesting a service quality assurance, the subscriber station informs the center station of the quality required for each service. The service quality request information includes an average rate of a service, a peak rate, a packet length, the upper limit value of a delay amount, and others. The center station allocates an identifier to a subscriber station according to a requested service quality. At this time, the center station can grasp the relationship between the identifier and the priority allocated to a service. It is not particularly required that the subscriber station grasps the relationship between the identifier and the priority allocated. Next, in response to reservation transmission permission information from the center station, the subscriber station transmits to the center station reservation information with an identifier according to the service of up-data to be transmitted. If there is up-data to be transmitted, the subscriber station calculates an up-band volume to be reserved. If there is no up-data, the subscriber station sets the up-band volume to zero. On the other hand, the center station allocates an up-band from data with higher priority in decreasing order of priority according to the service quality designated by the identifier of reservation information. If the reserved up-band volume is zero, the center station does not allocate the up-band. As described above, the center station allocates an identifier to a subscriber station according to the service quality required by the subscriber station while the subscriber station transmits reservation information using the identifier. Hence, the band can be flexibly controlled according to the up-service quality, without previously and fixedly determining the reservation information to priority relationship between the center station and the subscriber station.
In the multi-access communication system according to the second aspect of the invention, when receiving service quality request information from a subscriber station using a high service priority, the center station decides the transmission period of reservation solicitation information to be transmitted to a requested subscriber station based on the service quality request information. Thereafter, the center station transmits reservation transmission permission information to which a service identifier is added every transmission period determined. The length of reservation information generally is sufficiently shorter than that of the up-data while the use amount of the up-band is small. Hence, compared with the conventional method of periodically transmitting up-band allocation information to a subscriber station based on the service quality request information, it can be suppressed that the up-band is wastefully used even when the interval between pieces of up-data created by the subscriber station is varied. Since the center station transmits reservation transmission permission information only to the subscriber station requesting a service quality with high priority, the upper limit value of an up delay amount can be insured because pieces of up-reservation information such common data from subscriber stations do not collide with each other.
In the multi-access communication system according to the third aspect of the invention, the center station allocates a unique identifier to each subscriber station using a service with high priority as well as a common identifier to a subscriber station group using the service. Thereafter, the center station periodically transmits reservation transmission permission information with the common identifier to the subscriber station group using a service with high priority. The transmission period of the reservation transmission permission information is decided based on the service information from the subscriber station group using the same service. The subscriber station transmits reservation information to the center station only when there is up-data to be transmitted corresponding to the service of an identifier added to the reservation transmission permission information. If there is no up-data, the subscriber station transmits the reservation information. As described above, the reservation transmission permission information is periodically transmitted to a subscriber station group using the same service, using the common identifier, so that only the subscriber station with up-data to be transmitted returns the reservation information. As a result, the use efficiency of an up-band can be increased.
According to the multi-access communication system of the first, second or third aspect of the invention, in the multi-access communication system according to the fourth aspect of the invention, when the subscriber station starts the use of a new service, allocates a unique identifier, it informs the center station of the quality of the new service. The center station allocates a new unique identifier to the subscriber station as well as a common identifier to a subscriber station group using the same service. As described above, since the center station dynamically allocates an identifier for service to the subscriber station, the subscriber can make a request for an up-service quality at an arbitrary time. The center station transmits reservation transmission permission information while the subscriber station stops using a service, so that the use efficiency of an up-band can be improved.
In the multi-access communication system according to the fifth aspect of the invention, the center station selects the method of allocating an up-band according to a service quality required by the subscriber station. For example, in the case where a subscriber station asks for a delay amount as small as possible and where the packet length as well as variations in data generation interval of a subscriber station are small, the center station periodically allocates the up-band to the subscriber station. Although it is necessary to insure the upper limit value of a delay amount and where the packet length as well as variations in data generation interval of a subscriber station are large, the center station periodically transmits to the subscriber station the reservation transmission permission information to which a unique identifier is added. In the case where it is unnecessary to insure the upper limit value of a delay amount and where the packet length as well as variations in data generation interval of the subscriber station are large and where a small delay amount is required, the center station periodically transmits reservation transmission permission information to which a common identifier is added, to a subscriber station group using the same service. Finally, in the case where there is no request to a delay amount and where the band must be preferentially allocated to the common data in a congestion state, the reservation information is preferentially processed according to the identifier, without particularly performing the periodic transmission control by designating a service. As described above, the center station can flexibly allocate the up-band by selecting the up-area allocating method according to a service quality requested by a subscriber station.
In the multi-access communication system according to the sixth aspect of the invention, the center station measures an up-load received from a subscriber station and selects the up-band allocating method to the subscriber station according to the up-load. For example, when it is necessary to allocate an up-band preferentially to common data in an up-congestion state and to decrease the delay amount, the center station periodically transmits either up-band allocation information to the subscriber station or reservation-transmission permission information with a unique identifier to the subscriber station. When the up-load is middle, the center station periodically transmit reservation transmission permission information with a common identifier to a subscriber station group using the same service. Finally, in the case where the up-load is small and where the delay time of common data is sufficiently small, only the reservation information is preferentially processed according to the identifier, without particularly performing the periodic transmission control by designating a service. As described above, since the center station selects the up-band allocating method according to load conditions, the up-band can be allocated with high efficiency.